In some image forming apparatus such as a laser printer, an electrostatic latent image is formed on a surface of a photosensitive drum, and a toner is supplied onto the electrostatic latent image from a developer cartridge, so that a toner image is carried on the surface of the photosensitive drum. The toner image is then transferred onto a sheet, whereby an image is formed on the sheet.
The developer cartridge includes a casing that accommodates a toner and has an opening portion formed towards the photosensitive drum. The casing is provided with a developing roller rotatably provided so as to be exposed from the opening portion, a layer-thickness regulating blade that restricts a layer thickness of the toner carried on the developing roller, and a seal member that prevents the toner from leaking out of the both axial end portions of the developing roller.
For example, there has been proposed some developing device including a toner thin layer-forming blade having a projection made of a silicon rubber elastic body provided over the entire longitudinal width of a distal end of a thin plate spring, in which a first seal member is provided on each of both longitudinal end portions of the developing roller on an upstream side of the rotation direction of the developing roller with respect to the abutting position of the projection against the developing roller.
Further, there has been proposed some developer cartridge which include a leaf-spring member that is arranged in opposed relation to a developing roller and has a layer-thickness regulating blade formed of an insulating silicone rubber at its lower end portion, and a side seal attached to each of both lateral end portions of the leaf-spring member.
However, in the aforementioned developing device, the projection is provided over the entire longitudinal width of the toner thin layer-forming blade. A higher pressure is applied to the both longitudinal end portions of the toner thin layer-forming blade than to the center portion therebetween, so that the both longitudinal end portions thereof are more abraded than the center portion thereof due to rubbing by the projection. As a result, the disadvantage of toner leakage out of the longitudinal end portions thereof is induced.
Furthermore, in the aforementioned developing device described, the first seal member is disposed on the upstream side of the rotation direction of the developing roller with respect to the abutting position of the projection against the developing roller. Therefore, the disadvantage of toner leakage from the portion between the toner thin layer-forming blade and the first seal member is induced.
In the aforementioned developer cartridge, as shown in the representative drawing, both lateral end portions of the leaf-spring member is formed narrower along the rotation direction of the developing roller than the center portion therebetween. This can reduce the pressure applied to the both lateral end portions thereof by the narrowed portion. Further, the side seals are overlapped with and attached to the both lateral end portions of the leaf-spring member. This can suppress toner leakage from the portion between the leaf-spring member and each of the side seals.
However, the aforementioned developer cartridge may still slightly cause the toner leakage from the portion between the leaf-spring member and each of the side seals in some cases.